doc. RNDr. Libor Mrňa, Ph.D.
E-mail:   mrna@fme.vutbr.cz  Dept.:   Institute of Manufacturing Technology Dept. of Metal Forming and Plastics Position:   Associate Professor

Publications:

• ŘIHÁČEK, J.; MRŇA, L.:
  Comparison of Implicit and Explicit Algorithms of Finite Element Method for the Numerical Simulation of Hydroforming Process, MM Science Journal
  journal article in Scopus
• KUBÍČEK, J.; ŠMAK, M.; PODANÝ, K.; MRŇA, L.:
  Welded joint of high-strength steels Weldox 700 and common grade steel S 355, MM Science Journal
  journal article in Scopus
• MRŇA, L.; ŘIHÁČEK, J.:
  Využití laserového svařování při vývoji nového typu solárního absorbéru,
  Zváranie - Svařování, Vol.64, (2015), No.7-8/2015, pp.155-158, ISSN 0044-5525, Výzkumný ústav zváračský Priemyselný inštitút SR
  journal article - other
• ŘIHÁČEK, J.; MRŇA, L.:
  Forming a Structured Surface of a New Type of Solar Absorber with Hydroforming,
  Advanced Materials Research, pp.49-54, ISSN 1022-6680, Trans Tech Publications
  journal article - other
• MRŇA, L.; ŘIHÁČEK, J.; LIDMILA, Z.; PODANÝ, K.; KUBÍČEK, J.:
  Solární absorbér se strukturovaným povrchem – možná cesta ke zvýšení účinnosti.,
  Konference Alternativní zdroje energie 2014, pp.119-128, ISBN 978-80-02-02546-7, (2014), Společnost pro techniku prostředí
  conference paper
  akce: Alternativní zdroje energie 2014, Kroměříž, 01.07.2014-03.07.2014
• DOHNAL, I.; ŠLAIS, M.; FOREJT, M.; MRŇA, L.:
  Hopkinson Tensile Tests of Flat Specimens.,
  Journal of Mechanics Engineering and Automation, Vol.3, (2013), No.9, pp.560-565, ISSN 2159-5275
  journal article - other
• MRŇA, L.; FOREJT, M.; LIDMILA, Z.; PODANÝ, K.; KUBÍČEK, J.:
  Manufacturing of solar absorber by unconventional methods,
  Metal 2012, pp.1-6, ISBN 978-80-87294-29-1, (2012)
  conference paper
  akce: METAL 2012: 21st International Conference on Metallurgy and Materials, Brno, 23.05.2012-25.05.2012

List of publications at Portal BUT

Abstracts of most important papers:

• ŘIHÁČEK, J.; MRŇA, L.:
  Comparison of Implicit and Explicit Algorithms of Finite Element Method for the Numerical Simulation of Hydroforming Process, MM Science Journal
  journal article in Scopus
  This paper deals with numerical simulation possibilities of a hydroforming technology in production of a flow solar absorber with structured surface in a single technological operation. An austenitic stainless steel X5CrNi18-10 is used as a material for the production of the flow solar absorbers. In the theoretical chapters, comparison between implicit and explicit algorithms of finite element method (FEM) is performed. Experimental part of the paper includes creation of geometrical, material and computational models for the explicit and the implicit solution in software ANSYS Workbench and ANSYS LS-DYNA. Finally, due to evaluation of the experiment and FEM results, comparison between the implicit and the explicit theoretical solution of a formed part thickness is performed.
• KUBÍČEK, J.; ŠMAK, M.; PODANÝ, K.; MRŇA, L.:
  Welded joint of high-strength steels Weldox 700 and common grade steel S 355, MM Science Journal
  journal article in Scopus
  High-strength steels can be effectively utilized for strengthening existing structures or to improve highly stressed elements or structural details fabricated from lower grade steel. When used together with traditional grades of steel, the favourable mechanical properties of high-strength steels open up a wide range of applications in the steel constructions of civil and engineering structures, both in primary structural elements and in individual parts. The paper is concerned with butt and fillet welded joints of components made of high-strength steel with a yield strength of 700MPa and elements made of traditional grade S355 and S235 steel. The technique for welding materials with different strengths and the choice of additive materials for welding are presented in the experimental research.
• MRŇA, L.; ŘIHÁČEK, J.:
  Využití laserového svařování při vývoji nového typu solárního absorbéru,
  Zváranie - Svařování, Vol.64, (2015), No.7-8/2015, pp.155-158, ISSN 0044-5525, Výzkumný ústav zváračský Priemyselný inštitút SR
  journal article - other
  Design of solar absorber is recently settled to form absorbing plate with heat dissipation through a pipe register on the back side. The paper discusses the cushion solar absorber produced using laser welding technology, when the penetration of two plates, the required meandering structure providing controlled flow of heat exchange medium through the whole surface of the absorber. They have already made functional samples with dimensions of 1000x1000mm. It is also investigated the possibility of manufacturing the solar absorber with a structured surface - running jehlancovitých cavities in the front absorbent sheet. This construction increases the heat transfer area and in the cavities with the sunlight absorbed through multiple reflections. With this mechanism will reduce dependence on daily and annual running of incident solar radiation. Surface is produced hydroformováním.
• MRŇA, L.; KŘIVAN, M.:
  Technologie výroby deskového solárního aborbéru laserovým svařováním a nízkotlakým hydroformingem.,
  Kovárenství, Vol.2012, (2012), No.44, pp.101-104, ISSN 1213-9289, Svaz kováren ČR a.s.
  journal article - other
  Article deal with a proposal for a new design of flat solar absorber based on creation of proper meander structure for defined circulation of heat exchange fluid in the whole area of the absorber by method of laser welding of two plates of thin metal sheets. Consequently, using a low-pressure hydroforming this structure is blowed to the permanent deformation, and cavity is created for circulating heat exchange medium. In this case, the sunshine heat is absorbed in the heat exchange fluid directly and thus is not heat loses in comparison with pipe system of the "classical" flat solar absorber. Holes for connection to circulation system in thin sheet metal are created by the method of Flow drill.
• DOHNAL, I.; ŠLAIS, M.; FOREJT, M.; MRŇA, L.:
  Hopkinson tensile tests of flat specimen,
  The International Conference NEWTECH 2011 on Advanced Manufacturing Engineering, pp.79-83, ISBN 978-80-214-4267-2, (2011), BUT-FMI Institute of Manufacturing Technology
  conference paper
  akce: NEWTECH 2011, Brno, 14.09.2011-15.09.2011
  Plastic deformation of metallic materials and alloys is a complex process that depends on a number of factors with the effect of strain rate being of particular importance. Dynamical tests are used for determination of mechanical properties. The Split Hopkinson Tensile Bar Test is often used for these experiments. The present paper deals with possibilities of testing device for flat bars adapted at Hopkinson test. The aim of this work is concentrated on strain rate influence on 1.4301 austenitic steel too.